1. Field of the Invention
The present invention relates to a scanner device which reads film of a certain format and a control method thereof, and an image input system.
2. Description of Related Art
A known scanner device (Japanese Patent Laid-Open No. 5-145838) which handles two types of film, namely film strips and film stored in cartridges has been proposed.
Also, known scanner devices perform pre-scanning before main scanning for reading a film image in which the film image is read and parameters relating to exposure are set.
However, with known scanner devices, filters and the like must be used to perform color correction and the like before pre-scanning, depending on the format of film, such as negative film or positive film. However, known arrangements have required the operator to judge the type of film and mount the color correcting filters, and this have been insufficient in handiness of use with regard to this aspect.
Also, in the event of performing scanning of transparent originals such as photography film or the like, the original is irradiated by a light source, the transmitted light is converted into linear electric signals by means of a photo-electric converting device, and certain digital data is obtained by performing A/D conversion of these electrical signals. It is preferable to match the range of quantity of transmitted light (the intensity of transmitted light) with the range of quantity of convertible light of the photo-electric converting device as much as possible, in order to digitize the change in the quantity of transmitted light to the fullest extent effectively using the number of bits employed for this A/D conversion.
Generally, such scanning has been performed in two runs, pre-scanning and main scanning. First, a pre-scan is performed at low resolution. The conditions for this pre-scan is a single setting determined by the type of film, such as negative or positive. The pre-scan image thus obtained is displayed on the monitor as a preview image. The user observes this preview image, and manually sets brightness, tint, and so forth for the main scan, following which the main scan is executed. However, this above-described conventional method requires the user to make settings for each original that is to be subjected to main scanning, which means that in the event that a great number of images are to be handled a great deal of time is required, and the load on the user is great as well. According, a method has been conceived wherein the pre-scan image is analyzed by computer, and the computer automatically sets the scanning conditions fore the main scan based on those results. For example, the average brightness of the original is calculated from the pre-scan image, the luminous quantity of the light source is changed accordingly, thus adjusting the luminous quantity reaching the CCD. Or, according to this idea, the scan speed may be adjusted, so as to performed scanning appropriate for each original, so as to effectively obtain information recorded on the original.
The original is irradiated by the light source, the transmitted light thereof is converted into electrical signals which are linear as to the transmittance factor of the original by means of a photo-electric converting device, and A/D conversion of these electrical signals obtains digital signals. The digital signals obtained here are further converted into scanner output digital signals via a digital signal conversion table. This arrangement can handle film types such as negatives or positives by changing this digital signal conversion table. For example, methods for removing differing color balances according to the film type by means of manually selecting a plurality of digital signal conversion tables corresponding with each film stored in the host computer are being used in scanners actually on the market.
However, in order to effectively use the number of bits for A/D conversion, the output voltage from the concentration range to be obtained by the photo-electric converting device must be matched with the A/D conversion area. Known systems have used adjustment of electrical gain, offset, luminous quantity, etc. to set the A/D conversion range to match the concentration area of the original to be obtained. However, this destroys linearity to the concentration of the original, necessitating handling of such warped image data. This means that precise control of .gamma. correction to the original is difficult, and in the event of handling various negatives with differing exposure conditions, it has been impossible to perform appropriate .gamma. correction for each.